The present invention relates to an improvement in end-to-end connection of elongated concrete elements, preferably concrete piles intended for ground reinforcement and similar purposes, which elements are provided with reinforcement rods extending lengthwise through the element and which are joined together at their ends by means of connecting elements.
One technical field wherein various embodiments of end-to-end connections are applied is, as mentioned above, in piles which are rammed into the ground to improve the supporting ability thereof. According to previously known techniques various kinds of connecting elements have been utilized, each one of these elements simultaneously engaging or otherwise interconnecting two pile end shoes positioned in abutting relationship and for this purpose provided with notches, grooves or securement means of some kind of a shape corresponding to that of the connecting element.
The longitudinal reinforcement rods of the concrete pile are usually welded or screwed onto the end shoes.
After the end-to-end connection of two piles to secure them to one another, tension forces occurring in the piles will consequently spread out from the reinforcement rods of one pile by way of the end shoe thereof, the connecting element between this pile, and the adjacent end shoe of the other opposite pile and finally by way of the last-mentioned end shoe continue to the reinforcement rods of the second pile.
Independently of the kind of connecting element which is used in this type of end-to-end connection the latter suffers from considerable disadvantages because of the long path over which the forces are transferred from one concrete element to the next when flexural stress occurs in the joint, which leads to very disadvantages moments with consequential risks of breaks of the joint.
It has been found that welding the end shoes to the reinforcement rods in concrete piles makes the reinforcement quite unflexible. When interconnected piles are exposed to impact while being rammed into the ground, the concrete layers closest adjacent to the end shoes usually are reduced to powder. As a result, at the end of a series of blows from the pile-driver, the end shoes have a tendency to move somewhat in the longitudinal direction of the piles relative to the reinforcement rods. Should such relative movements not be possible because the reinforcement rods and the end shoes are securely anchored to each other, such a non-flexible joint often would result in bending of the reinforcement rods immediately internally of one or several of the end shoes, and in several cases the concrete pile will be cracked open on one side. This is, of course, quite satisfactory.